The present invention relates to cold-applied elastomeric-type polyurethane joint sealing compounds for sealing, caulking and glazing operations in building construction and more particularly to non-sag sealants which provide soft low-modulus elastomers suitable for vertical joints and other joints subject to extreme variation in width.
Since 1965 polyurethane joint sealants have been used extensively in the elastomeric sealant industry because of their quality and economy as compared to other sealants. These have functioned satisfactorily in joints whose movement is small. However, the joint widening and closing is a serious problem when the variation in width of the joint is substantial, such as 20 to 25 percent or more, because of the large tensile forces applied to the sealant which can cause adhesive failure or failure of the sealant material itself.
To avoid such failure in joints subject to large variations in width, particularly those frequently changing width due to temperature changes and the like, it is necessary to provide a soft low-modulus elastomer with excellent tensile and elongation properties and excellent weathering properties. This is less of a problem in highway joints where the sealant can be poured in place because non-sag properties are less important. In vertical joints between the concrete panels of a modern building, the problem is very serious because of the importance of sag resistance. If a caulking gun is used, the problem is even more difficult because of the need for good flow properties.
A simple approach to the problem of sealing joints subject to severe variations in width is to employ a non-sag elastomeric-type silicone caulking composition which produces a soft low-modulus elastomeric product. One-component silicone joint sealants are suitable for this purpose but are relative expensive and energy wasteful, have poor tear tear resistance, tend to collect dirt, and cannot be painted.
There is a one-component moisture-curing polyurethane joint sealant made by a Swiss company (SIKA) which employs polyvinyl chloride to achieve non-sag properties without an undue increase in the durometer hardness of the cured sealant. This type of sealant which is disclosed in U.S. Pat. No. 4,059,549, has poor package stability and poor adhesion to water-soaked masonry, and is more difficult to prepare than more conventional polyurethane sealants.* FNT * See Table I on page 30
There is also a two-component epoxy-type polyurethane joint sealant. It has been on the market for many years under the name "DYMERIC" and is disclosed in U.S. Pat. No. 3,445,436, filed June 14, 1966. This two-component sealant has non-sag properties and when cured has a low modulus (e.g., A Shore A durometer hardness of 45 or less) comparable to that of the SIKA sealant but has poor adhesion to water-soaked masonry and requires mixing on the job.* FNT * See Table I on page 30
It is preferable to employ one-component sealants and to avoid the extra time and expense involved in mixing two components at the point of use. One-component non-sag moisture-curing polyurethane caulking compositions have been very popular for simple joint sealing operations because of the economy of application, but they present an extremely difficult problem to the compounder. Prior to the present invention, it has not been possible to provide a low-modulus one-component polyurethane sealant of the desired softness with, at the same time, the desired sag resistance and flow characteristics which could be easily manufactured and which meets the federal specifications for Class A cold-applied elastomeric-type joint sealants. Such federal specifications were developed more than a decade ago by the National Bureau of Standards and are set forth in Federal Specifications TT-S-00227B and TT-S-00230C.
Except for the above-described sealants of U.S. Pat. Nos. 3,445,436 and 4,059,549, there was no non-sag polyurethane joint sealant available prior to this invention which could meet such federal specifications for a Class A rating. The known polyurethane sealants could not meet the Class A requirements because they had excessive durometer hardness (e.g., a Shore A durometer hardness of about 60 or greater) when compounded to provide the necessary non-sag properties. Manufacturers of caulking compositions unable to obtain such Class A rating were often unable to sell their product because contracts involving Government construction projects required Class A sealants meeting the federal specifications.
Conventional compounding techniques make it possible to vary the elastomeric properties and flow properties of a polyurethane sealing composition, but it has heretofore been impossible to achieve the desired combination of extrudability, non-sag and low-modulus merely by judicious choice of compounding ingredients or fillers.
Conventional fillers and reinforcements for polyurethanes and plastics, such as silica, talc, calcium silicate, Wollastonite, Asbestine, kaolin, barium sulfate, graphite, hydrated alumina, chrysotile, serpentine, pearlite, vermiculite, mica, crocidolite, zirconium silicate, barium zirconate, calcium zirconium silicate, magnesium zirconium silicate, glass beads, fiberglass, titanium dioxide, PMF mineral fiber, nylon fiber, polyester fiber, alpha cellulose fiber, polypropylene fiber, and the like provide no solution to the problem. Those which are satisfactory fillers for a joint sealant do not provide the desired combination of low-modulus and non-sag properties when used alone or in combination with other conventional fillers. It has heretofore been generally accepted that mixing of different fillers provides no synergistic result and is of no particular consequence when seeking such a combination of properties. This is also true of the conventional fibrillar fillers such as Wollastonite, fibrous talc, asbestos, and processed mineral fiber (PMF).
Fibers used for reinforcing polyurethane products such as glass fibers, nylon fibers, polyester fibers, polypropylene fibers and other synthetic fibers are generally unsatisfactory for polyurethane joint sealants, and particularly one-component caulking compositions. They have poor compatibility and do not disperse properly, and they produce a coarse surface which is unattractive and unacceptable. For these reasons, they have not been used in joint sealants.
Another fiber material, which has hitherto not been used in sealants, is synthetic wood pulp fiber. For many years synthetic fibrillar polyethylene and polypropylene fibers have been produced as a substitute for cellulose fibers with various fiber lengths from 0.7 to 2.5 millimeters or more. These synthetic wood pulp fibers, sold under the name SWP, have been used for various products such as wallpapers, packaging papers, electrical paper, cigarette filters, photographic paper, molded products, masonry cement, body-molding compounds, roofing compounds, traffic paints, plaster repair, non-woven fabric, texture paints, and the like.
Prior to this invention, SWP fibers have been tried in polyurethane joint sealants and other polyurethane compositions and found unsatisfactory particulary because of poor compatibility, excessive sweat out and unacceptable surface quality in the cured product. The fibers tend to project beyond the surface of the cured sealant and provide a coarse surface that is unacceptable.